When a plurality of diesel engine driven generators are connected for parallel load operation, an automatic load distributing apparatus is provided to make loads on the respective generators substantially even. FIG. 8 is for explaining general construction of an automatic load distributing apparatus which is frequently used for conventional generators driven by diesel engines with Bosch fuel injection pumps.
Upon parallel load operation of such generators, a first diesel engine driven generator 20a and a second diesel engine driven generator 20b are arranged in parallel. The first diesel engine driven generator 20a is connected to a bus bar 23 via a wire 21a and a first breaker 22a. The second diesel engine driven generator 20b is also connected to the bus bar 23 via a wire 21b and a second breaker 22b.
The first diesel engine driven generator 20a is constructed of a first engine 24a, a first generator 25a, a first load distributing unit 26a, and a first rotational speed controller 27a. The second diesel engine driven generator 20b is of the same construction as the first diesel engine driven generator 20a and the description thereof is omitted below by labeling respective elements with corresponding reference numerals.
The first engine 24a is constructed of a first Bosch fuel injection pump 28a, a first governor 29a, a first actuator 30a, and a first rotational speed sensor 31a. A control lever 32a, installed on the first governor 29a, and a lever 33a, installed on the first actuator 30a, are connected by a rod 34a. The first actuator 30a and the first rotational speed controller 27a are connected by a wire 35a; the first rotational speed sensor 31a and the first rotational speed controller 27a are connected by a wire 36a.
The first load distributing unit 26a is connected to the first rotational speed controller 27a via a wire 37a, and to bus bars 38 and 40 of parallel line via wires 39a and 41a, respectively. The first load distributing unit 26a and the first generator 25a are connected via both a voltage detecting wire 42a and a current detecting wire 43a.
Hereinbelow, the description will be made first of a single load operation of the first generator 25a in the first diesel engine driven generator 20a, and then to a parallel load operation of the first generator 25a and the second generator 25b in the second diesel engine driven generator 20b.
First of all, the single load operation of the first generator 25a is described with reference to FIG. 2. FIG. 2 shows the rack position of the first fuel injection pump 28a in ordinate and the rotational speed of the first fuel injection pump 28a in abscissa. The rack position in the ordinate has one to one correspondence to the load factor of the output of the first engine 24a. Indicated from an operating point a to an operating point b is the upper limit of the rack position, which corresponds to 100% of the load factor. An operating point j indicates a rated output/rated rotational speed of the first engine 24a. Indicated from the operating point b to an operating point c is an actual range of use, which corresponds to an operating range of the first governor 29a. A rated rotational speed A is determined by the number of electrodes and the frequency of the generator in the case of an engine for the generator, where the engine is operated at constant rotational speed.
Upon no-load operation after completion of engine warm-up, the rack position is at an operating point c. Then when the first generator 25a is connected to the bus bar 23 by turning the first breaker 22a "ON" and a load, e.g., of 80% of the generator rated output value, is applied to the first generator 25a from the outside, the first governor 29a acts to transitionally move the rack position from the operating point c to an operating point d. At the same time, the amount of fuel injection to the first engine 24a, and hence its output power, increases. However, the rotational speed at the operating point d is decreased by B from the rated rotational speed A, and needs to be increased to an operating point e.
The increase in the rotational speed from the operating point d to the operating point e is controlled by the first rotational speed controller 27a. In this case, an engine rotational speed signal from the first rotational speed sensor 31a is inputted to the first rotational speed controller 27a via the wire 36a. Upon receipt of the signal, the first rotational speed controller 27a sends a signal corresponding to the increased rate B of the rotational speed to the first actuator 30a via the wire 35a to move the lever 33a on the first actuator 30a in a direction of "INCREASE" in rotational speed, and hence the control lever 32a via the rod 34a. Thus the rotational speed is increased, and the single load operation of the first generator 25a is carried out at the operating point e by an engine output corresponding to a load of 80% of the rated output value of the first generator 25a.
Next, a parallel load operation of the first generator 25a and the second generator 25b will be is described with reference to FIGS. 3 and 4. As an example, the description is made to a case where the first generator 25a is operated while gradually decreasing its load from 80% to 40% and the second generator 25b is operated from an unloaded condition while gradually increasing its load from 0% to 40%.
The 80% loaded operation of the first generator 25a is indicated at the operating point e in FIG. 3; the unloaded operation of the second generator 25b is indicated at an operating point g in FIG. 4. From this operating condition, the second breaker 22b is turned "ON" to connect the second generator 25b to the bus bar 23 so as to start parallel load operation.
A comparison between the 80% load factor of the first generator 25a and the 0% load factor of the second generator 25b is made by the first load distributing unit 26a and the second load distributing unit 26b. In this case, an output signal from the first generator 25a is inputted to the first load distributing unit 26a via the voltage detecting wire 42a and the current detecting wire 43a. At the same time, an output signal from the second generator 25b is inputted to the second load distributing unit 26b via the voltage detecting wire 42b and the current detecting wire 43b. Then, an output signal from the second load distributing unit 26b is inputted to the first load distributing unit 26a via a wire 41b, the bus bar 40 of parallel line, and the wire 41a. The first load distributing unit 26a compares the output signal corresponding to the 80% load factor of the first generator 25a with the output signal corresponding to the 0% load factor of the second generator 25b and processes the comparison result to output a signal to the first rotational speed controller 27a so as to reduce the rotational speed of the first engine 24a. The first rotational speed controller 27a performs control, using the signal for reducing the rotational speed of the first engine 24a and a signal from the first rotational speed sensor 31a to send a signal corresponding to a rotational speed drop rate C to the first actuator 30a via the wire 35a. This signal moves the lever 33a on the first actuator 30a in a direction of "DECREASE" in rotational speed, and hence the control lever 32a via the rod 34a. Thus the engine speed is reduced.
The second generator 25b is also operated in a manner similar to the first generator 25a to increase the engine speed.
Through the above operation, the load factor of the first generator 25a is gradually decreased from 80% to 40%, the load factor of the second generator 25b is gradually increased from 0% to 40%, and they are finally made to be equivalent. In other words, the loaded condition of the first generator 25a in FIG. 3 is gradually decreased from its 80% load factor at the operating point e to its 40% load factor at an operating point f, while the loaded condition of the second generator 25b in FIG. 4 is gradually increased from its 0% load factor at the operating point g to its 40% load factor at an operating point h. Thus, the loads are automatically evenly distributed on the engines for the first and second generators 25a and 25b at a load factor of 40%.
Such a conventional technique, however, causes the following problems with the first and second load distributing units 26a and 26b.
(1) The loads for the first and second generators 25a and 25b are detected as signals from the generators. Since such outputs are too large, the voltage and current signals are necessarily drawn through respective transformers. Further, since the wiring is of a three-phase type, a total of six wires, three for voltage plus three for current, is required. This increases the number of assembling steps associated with the wiring on the outgoing side of the first and second generators 25a and 25b and the side of the first and second load distributing units 26a and 26b, and makes the entire construction complicated in cooperation with the provision of the transformers required for drawing voltage and current signals.
(2) If the apparatus is designed to obtain loads on the first and second generators 25a and 25b at a high voltage, such as 400 volts, without transformers, there is a danger of shock due to mishandling in maintenance and outfitting operations. Such a case requires skilled technical experts to work.
(3) Since the control apparatus for the first and second generators 25a and 25b is divided into a group of the first and second load distributing units 26a and 26b and a group of the first and second rotational speed controllers 27a and 27b, it occupies a large space. Mounting brackets are also required for respective control components, and hence the number of assembling steps is increased.
(4) Assuming that the first generator 25a is a 400-kilowatt generator and the second generator 25b is a 200-kilowatt generator, voltage and current transformers for 400 kilowatts and 200 kilowatts need to be mounted respectively on the first generator 25a and the second generator 25b when both generators are connected for parallel load operation. In this case, when the transformer for 400 kilowatts is incorrectly mounted on the second generator 25b like the first generator 25a upon parallel load operation, the respective load factors of the first and second generators remain uneven. If a load of 450 kilowatts is applied from the outside during the parallel load operation, the first generator 25a is loaded at 225 kilowatts and its load factor is 56.3%, while the second generator 25b is loaded at 225 kilowatts and its load factor is 112.5%. As a result, the second engine 24b for driving the second generator 25b exceeds its rated power and has operational problems.